Process of making an imaging scintillation chamber



3 5 9 a 2 5 S I awn XR 3,507,734 v April 197% I. w. RUDERMAN 3,507,734

U PROCESS OF MAKING AN IMAGING SCINTILLATION CHAMBER I l 3 Original Filed April 5, 1961 X57 INVENTOR. 73 [lb 4865M Erase/v4 H BY 2% :k; V

4rrae/vzr 1961. This application Feb. 26, 1965, Ser. No. 441,953

Int. Cl. B32b 31/00 US. Cl. 156-268 ABSTRACT OF THE DESCLOSURE An imaging chamber, for providing a visible light out put in accordance with the pattern of radiant energy incident thereon, is fabricated by adherently applying to one major face of a single scintillating crystal a backing layer of support material capable of passing the incident radiant energy; slitting the crystal from the opposite major face to a plane spaced slightly from the face to which the backing layer is applied, to form an array of elongated, longitudinally coextensive, linear, parallel scintillating filaments all joined together at a common end, each of the' filiiments being of uniform cross-section throughout its length and each having a length in the range from about 5 to about 20 centimeters and a maximum width in the range from about 0.1 to about 0.5 millimeter, the filaments separated from one another by the relatively narrow slots of parallel opposing side walls produced by the slitting step; andggoatin the longitudinal-surfaces of u the filaments with an ad titinat'e'r'ial capablggi blocking the transmission at siblejght thetetliiough, while leaving thend surfaces oi th filaments ojiposite the common end juncture free of any coating capable of blocking visible light, to permit passage of visible light, produced upon scintillation of the crystal filaments, via the free end surfaces and to prevent lateral passage of the visible light so produced via the longitudinal surfaces of the filaments.

This invention relates to observation, detection, or recording of flaws, defects or voids in solid materials such as regular or irregular bodies, plates, or strips of any material whereof such flaws, defects or voids differ in transmission of X-rays or gamma rays from the main body of the material. It is particularly adapted to be used in conjunction with apparatus to quickly test for existence of flaws in bodies of irregular shape such as engine parts.

This application is a continuation of my co-pending application, Ser. No. 100,142, filed Apr. 3, 1961, and now abandoned. i i

In the current art it is known to irradiate objects with X-rays or high energy gamma rays and to produce a shadow image of the body on X-ray film. Such procedure has the advantages of high sensitivity, good definition, and ease of producing a permanent record. However, it has the disadvantage of requiring much time and effort in the exposure and development of the film with consequent delay in obtaining the final result. In examining a large number of similar objects each must be identified with-its film. Also film is less sensitive to high energy X-rays and gamma rays than those of low energy; hence for examining the large bodies useful for numerous purposes-it is less effective as well as slower than desired. Furthermore, a static method such as X-ray inspection is insensitive to cracks in the inspected material when the crack is viewed across its thickness rather than edgewise. Thus, a crack of considerable width but extremely small thickness, such as may frequently occur, may be dis- 5 Claims aired rates Patent i 3,507,734 l atented Apr. 21, 1970 covered only with dilficulty or not at all. In the case of --added delayand complexity of equipment needed is undesirable or prohibitive.

Furthermore, in many manufacturing processes parts are produced which must be examined accurately and rapidly before being accepted for further manufacture or assembly.

Consequently, among the objects of the present invention are to increase the speed of accurate inspection of objects for flaws; to enable rapid inspection of different parts of bodies of regular or irregular shape, in more than one direction if desired; to accomplish visual inspection; and to achieve these and other desirable objects by producing an instantaneous dynamic image of the shadow of an opaque object including flaws therein, if any.

An exemplary fiaw detector system including ap aratus according to the invention comprises a source of X-rays or energetic gamma raysf'a scintillation crystal body, means for supporting a body to be tested adjacent to the crystal body so that the rays pass through it on the way to the crystal, and a mirror placed at an angle to the face of the crystal through which the face of the crystal may be viewed from a shielded position. For viewing the image of the body being tested on the face of the crystal one may use the eye but a more facile and effective means whereby an enlarged and intensified image may be viewed is to view the face of the crystal through a television camera and conduct the resultant pulses with suitable amplifications over a closed circuit television system to a television receiver. Among the scintillation crystals employable for this purpose are sodium iodide, cesium iodide and potassium iodide in each case activated with a small proportion of thallium. The essentially white light given ofi by cesium iodide thus activated seems advantageous. but numerous kinds of scintillating crystals may be used. A thin crystal, for example, a few millimeters to "a few centimeters thick and of large area such as 50 to several hundred square centimeters will give a visible image which can be viewed directly.

The resolution of defects by this type of crystal is somewhat rough but at high energies is improved.

For improving the resolution a luminescent imaging chamber constitutes an important feature of this invention. This consists of a multiplicity of closely packed parallel long and thin prisms or cylinders. These are of small diameter of the order of 0.1 to 0.5 mm., if circular, and of the same order of magnitude of cross section, it prismatic, and of a suitable length up to ten or more centimeters. They are so placed as to receive the X-rays or gamma rays in one end and to emit light on the other end. The image produced at the exit end of the light will give an image of an object being examined with a fineness or resolution dependent upon the degree of smallness of diameter and cross section of the prisms or cylinders of scintillating material. For many purposes and in the present state of the art of image intensifiers a cross section of 0.25 square millimeter would be satisfactory.

Further elucidation of exemplary. embodiments and methods of the invention will be made by reference to the accompanying drawings wherein:

FIGURE 1 comprises a schematic diagram of apparatus embodying the invention;

FIGURE 2 is a cross section on the line 22 of FIG- URE l illustrating the construction of the imaging chamber when it consists of a muttitude of closely packed .circulanfilaments of scintillating material;

' FIGURE 3 illustrates an embodiment consisting of closely packed square scintillating prisms which may be constructed as hereinafter described;

FIGURE 4 is a cross-section of the scintillating prisms of FIGURE 3 taken in the line 44; and

FIGURE 5 illustrates dia rammatically means for moving a strip or sheet cons 'ng of or hearing bodies to be tested in front of and immediately ad acent to a scintillator body or imaging chamber.

With reference to FIGURE l, a source 1 of. Xrays or gamma radiation is projected through an opening 2 ,in a shield 3 upon and through an object 4 to be examined. The rays are proportioned in energy to the thickness and nature of the object to be examined whereby the proportion emerging is a function of the thickness of the object and an X-ray or gamma ray image of the object with defects. if any. will be projected on the scintiljlator body or imaging chamber 5.

The X-rays or gamma rays proceeding from the point 1 to the specimen 4 are indicated as coming from a point source. This will be satisfactory in some cases if the source is sufiiciently far from the specimen 4 so that the irays are almost parallel. The rays may proceed from a field source. In any case they should have an approximate parallelism upon arriving at the specimen 4. t A shield 7 shields an observer or a television camera :8. When the camera is used it views the face of the crystal body 5 by means of a suitable mirror 9 which may be plane, concave, convex or otherwise curved as may be required or desired but, for exemplary purposes may be considered plane. The usual image orthicon tube, scanning and transmission circuit 11 serves to transmit pulses representing the image to the television receiver 11 where the image may be viewed on the screen.

The side of the crystal 5 adjacent the object 4 may be lightly silvered, tinned or aluminized to prevent exodus of light toward the specimen. Its outer lateral surfaces may be blackened.

Obviously, light generated in the crystal 5 may spread in all directions. Thus, unless the crystal be quite thin the image on the output side may be insufliciently refined. To correct this is one of the major objects of the invention and a luminescent imaging chamber is employed. In one form of this chamber polished scintillator filaments are employed. These are of small cross sections to give good definition, i.e. O.l to 0.5 millimeter in diameter. and of considerable length to have a high stopping power for gamma rays of large energy, i.e. 5 to 20 centimeters. For forming such filaments organic scintillating compositionshreiwith present techniques, more easily made but in other respects not as effective as crystals of activated sodium. cesium and potassium iodides, for exampte. As exemplary for the purpose one may use naphthalene or one of the scintillating compositions described in my patent application, Ser. No. 304.119 filed Aug. 13, 1952 issued as Patent No. 2,96l.54l dated Nov. 22, 1960. These filaments may be drawn 'OI'VIQI'IIICCI in any suitable manner. The'irdiiteral surfaces maybenaturally reflecting othaflight generated therein will ansmitted in a dowiitvar d direction, as per FIGURE 1. This tendc'ncy m'ay'be' increased by pol'tshing rn e tallizingmr blackening the surfaces before bundling them together. They may collected into a self supporting closely packcd lnrndle polished and optically insulated individuallyor by being encased in .1 block or o her suitable plastic masses illustrated in FIGURE 2, wherein the filaments 13 are supported in a plastic mass 14. FIGURE 2 is diagrammatic and intended to illustrate the principle rather than to shown actual numbers, spacings, and relative diameters of the filaments with respect to spacings. They may be packed in hexagonal ather than square array. The filaments need not have a circular cross sectio h but may be oval or have any suitable cross section provided they closely approximate being straight, paral-. lel, and each is reasonably uniform in diameter through out its length.

FIGURE 3 and 4 illustrate another form of imaging chamber. This may be made from a large scintillating crystal manufactured in the usual way. It may be mounted, for example, by cementing to a backing plate 15 composed of strong plastic, or thin light metal which ofi'crs slight resistance to the passage of gamma type rays. It my then be sawed almost or entirely to the bottom in a series of parallel slots 16, and another series 17 at approximate right angles to the first series. Thus. creating an array of small long narrow prisms of considerable length. Before cementing the surface next to the backing 15 and the outside surfaces may be metallized to produce a refiective inner surface. The side and top surfaces may also be metailized. Because of the method of manufacture the scintillating material used for this purpose may be chosen for the characteristics, among others, that it has the mechanical properties enabling it to be sawed or slit by convenient methods and for this reason the organic as well as inorganic scintillating substances mentioned hereinbcforc as well as other may be chosen. Most of them can be slitted by sawing.

The slots 16 and 1'7 may then be filled with black paint containing, for example, carbon black, lead sulfide or lead oxide tlbO) or mixtures, which is allowed to harden. Other substances may be used to prevent the passage of light laterally from one prism to another. For example, with thallium activated cesium iodide the paint might have the approximate density of the crystal.

Another method of manufacturing a luminescent imaging chamber resembling FIGURES 3 and 4- and which could be either rectangular or circular in cross section is to make a grid resembling the two sets of Slots of FIG- URES 3 and 4. This may be made of sheet metal or cast into shape from aluminum or other suitable metal or alloy. It would resemble one side of a sheet of honey comb having square cells but a hexagonally celled give could be used if desired. Another method would be to stack together a multitude of circular square or hexagonal tubes, mount them on a base such as base 15 with a reflective surface, then till the entire assembly y'ith plastic scintillating materiaTirTdipolyiiie -ize it lllfilttl ZIC- cording cribed in my patent above mentioned. Thus, each tube would be filled with a separate transparent body of eintillating material. In the case of circulartubes the spa es'between the tubes would have a cross section resembling a hypocycloid of four cusps. These could also be filled with scintillating material. This would not impair the efiicieney of the device but. would improve it by making better use of the available space and thus improve the resolution or fineness of definition of the device being examined. The circular prisms would then be interspersed with hypoeycloidal prisms of scintillating substance all bounded by reflective opaque sides.

In every case it may be desirable that the face of the scintillating material next to the specimen 4 be coated or otherwise provided with a reflective or blackened coating (easily penetrated by gamma rays) to prevent the exit of light from the material toward the specimen 4. In the other hand the face toward the mirror 9 should be polished or otherwise designed to emit the maximum amount of light.

FIGURE 5 is a diagrammatic representation of an arrangement for scanning a moving strip 18 for flaws. The strip may be guided over power driven rollers 19 above the imaging changer 5 and thus takes the place of the specimen 4 in FIGURE 1. The other equipment is in accordance with FIGURE 1. Consequently, a moving image of any perceptible flaws in the strip 18 would be observab e on .llC viewing tub" l2. Discrete bodies may be moved over the image changer 5 for examination as well as a continuous strip 18.

For the purposes of this specification the elongated prismatic or cylindrical elements of scintillating material, such as 13, and the elements bounded by the slots 16, 17, and others described herein or equivalent in function thereto, regardless of their cross-sectional shape, or mode of manufacture will be characterized as luminescent or scintillating filaments; an assembly'of them will be designated an imaging chamber. It is to be understood that their number and cross section will be chosen to adequately resolve or define the object under inspection and their length will vary according to the energy of the gamma or X-rays to be stopped and in accordance with the stopping power of the particular scintillator material or materials of which they are composed. In general, the results will be better as they have higher luminescent eificiency, low self-absorption of light, better optical homogenity, more effective optically insulated lateral surfaces, long lengths, minimum curvature along axes parallel to their length, short decay time for fluorescence, stability to their environment with time, suitable mechanical strength, high stopping power for gamma radiation.

Such practical details as supporting elements, means for shielding the luminescent imaging chamber 5 from extraneous light, means such as a casing and transparent cover for protecting the luminescent material from the air or moisture, when required, and other details are all considered to be within the skill of the art and have been omitted to simplify the attached drawings and foregoing text.

As used herein light or spectral light signify radiant energy in or near the visible region of the frequency spectrum, and optical refers to such light or energy or the properties of bodies with respect thereto.

The expression image of an object is used herein as synonomous with image of the shadow of an object.

There has thus been disclosed means for and method of producing a dynamic instantaneous image of the interior of an opaque object free of all delay in exposure time, developing time and handling time and otherwise fulfilling the objects of the invention.

What I claim is:

1. The method of fabricating an imaging chamber for receiving radiant energy of Wavelengths outside the visible region of the electromagnetic spectrum, said method comprising:

adherently applying to one major face of a single scintillating crystal a backing layer of support material capable of passing radiant energy of wavelengths to which said imaging chamber is torespond, slitting said crystal from the major face thereof opposite said one major face to a plane spaced slightly from said one major face to form an array of elongated, longitudinally coextensive, linear, parallel scintillating filaments all joined together at a com;- mon end, each of said filaments of uniform crosssection throughout its length and each having a length in the range from about 5 to about 20 centimeters and a maximum width in the range from about 0.1 to about 0.5 millimeter, said filaments separated from one another by the relatively narrow slots of parallel opposing side walls produced by said slitting, and i coating the longitudinal surfaces of said filaments with an adherent material capable of blocking the transmission of visible light therethrough, while leaving the end surface of each filament opposite said common end free of any visible light-blocking coating, to permit passage through said end surfaces of visible light produced upon activation of said scintillating filaments by said radiant energy received via said backing layer and to prevent lateral passage of said produced visible light from one filament to another via said longitudinal surfaces thereof.

2. The method according to claim 1 wherein said slitting is performed to produce a first plurality of said slots oriented in spaced parallel configuration and a second plurality of said slots oriented in spaced parallel configuration intersecting said first plurality of slots.

3. The method according to claim 2 wherein said second plurality of slots is oriented perpendicularly to said first plurality of slots.

4. The method according to claim 1 wherein said one major face is coated, prior to application of said backing layer, with a material capable of reflecting visible light and of passing said radiant energy of wavelengths to be received by said imaging chamber, to prevent passage Of said produced visible light via said one major face in the direction of the received radiant energy.

5. The method according to claim 1 wherein said coating step is performed by filling said slots separating said filaments with material opaque to visible light.

References Cited UNITED STATES PATENTS 2,829,264 4/1958 Garrison 250-71.5 2,992,331 7/1961 Bonner et a1. 25071.5 3,032,657 5/1962 Meier et al. 25071.5 3,048,698 8/1962 Carlson 250-715 3,110,816 11/1963 Kaisler et a1. 250-71-\5 3,225,193 12/1965 Hilton et al. 250-71.5

JULIUS FROME, Primary Examiner A. H. KOECKERT, AssistantExaminer US. Cl. X.R. 

